Faris approaches her role as an erstwhile Playmate who makes over a bunch of nerdy sorority girls with wholly unwarranted enthusiasm and an altogether winning lack of guile.

It probably doesn’t hurt that she spends most of the movie in short shorts and a halter top.

“Legally Blonde” scribes Karen McCullah Lutz and Kirsten Smith are credited with the barely-there screenplay, which cribs from their previous effort, as well as from “Animal House” and many more obscure sources, including a Tommy Lee Jones comedy called “Man of the House.”

Faris plays the naive Shelley, who’s cast out of the Playboy Mansion – Hugh Hefner has a substantial supporting role as “himself,” surrounded by siliconed wonders – the day after her 27th birthday (“59 in bunny years”).

After spending the night sleeping in a car, she stumbles onto a college campus, where she is improbably hired as the house mother by the hopelessly nerdy girls of Zeta Alpha Zeta. (The initials are a dubious homage to the team of ’80s comedy directors responsible for “Airplane!”)

Despite the skepticism of the girls – particularly a much-pierced feminist Goth chick winningly played by Kat Dennings – Shelley throws herself into the job, raising money for charity by washing cars, throwing a wild party and helping the girls discover their inner hotties.

The girls include Emma Stone – a Lindsay Lohan look-alike seen to better advantage in “The Rocker” – as the sorority president with bottle glasses, Rumer Willis (Bruce and Demi’s daughter) as a sister in a full body brace, and even more grotesque stereotypes.

Colin Hanks doesn’t have much to do as an unlikely nursing-home owner who serves as Shelley’s very nominal love interest.

This is pretty much a one-woman show for Faris, and she doesn’t get much help from director Fred Wolf (the execrable “Strange Wilderness”). Even the movie’s best gag – a takeoff on a famous scene with Marilyn Monroe that’s in the trailer – is spoiled by explaining what’s being spoofed.

Here and there, Faris gets a good line – standing naked (sorry, guys, you see her back only) before the horrified sisters, she shows off what “God and Dr. Borkman gave me.”

But mostly the actress bats her eyelashes and works wonders with groaners: “A brothel? I’m not trying to make soup,” “I even let Bob Saget grind on me during a slow dance,” “The eyes are the nipples of the face,” and “My heart’s pounding like a nail.”